1. Field of the Invention
The invention relates to a brake device for at least one axle of a wheel of a vehicle.
2. Description of the Related Art
German patent 1,069,019 discloses an actuating device for a mechanically actuated inside shoe brake for vehicle hubs, showing the conventional principle of a brake shoe arrangement which can be used for brakes for lightweight vehicles. The two brake shoes widen against a spring force by means of a rotatable cam and rotate about a rotation point in such a manner that the brake shoes come to bear against the brake drum. Since the leading brake shoe has a higher braking action than the trailing brake shoe, the wear to this brake is greater, and consequently, after a period of use, the lining heights on the two brake shoes differ, causing distortion to the cam which is actuated by the brake lever. Since the rotation point between the brake shoes and the cam in each case has a rotation point fixed on a brake plate, it is not possible to form a balance between the two brake shoes with respect to the pressure which they exert on the brake drum. As the wear increases, the brake will lose braking force, since the trailing brake shoe will increasingly have to provide the braking force.
The above-described drawback relating to the balancing of the brake shoes in terms of their contact with the brake drum is avoided by a multishoe brake, as described in German Patent No. 949 329, which is preferably designed as a two-shoe inside brake, in particular for motor vehicles. The multishoe brake has a centering device for the brake shoes in the at-rest position. The brake shoe ends face one another and are separated by a spreading member. The shoe ends are connected to one another by a restoring spring which acts as a centering device and is supported approximately in the center, radially with respect to the drum, on a fixed frictional body. The spreading member is connected to a brake shaft on which a brake lever for actuating the multishoe brake is arranged, via a dovetail-like guide, acting displaceably in the direction of force of the two brake shoes. The rotary movement of the brake shaft is transmitted to the spreading element via the dovetail, and the braking action, due to the contact of the brake shoes with a brake drum, can take place without obstruction and, in particular, always with the same contact force. As the wear increases, the leading brake shoe, with its greater wear, can in this way be adjusted to a greater extent than the trailing brake shoe, which exhibits a lower level of wear. Therefore, the braking action will not change compared to the above-described brake in accordance with German patent 1,069,019.
The brake device of the invention, which is also suitable for braking a brake drum which is connected to a wheel of a bicycle, represents an advanced development over the prior art, in which in particular the simplifications to the designs of the brake shoes and the design of the cam in conjunction with a brake lever contribute to producing a brake device which is inexpensive.
The brake device has a shoe element which is connected to a holder, it being possible to connect the holder to a brake carrier in such a manner that the shoe element is simultaneously centered on the brake carrier. The shoe element is of similar design to an inside band brake and preferably has a brake lining over its entire periphery. The holder is connected to the shoe element at a connecting point in such a manner that the shoe element has two free shoe halves which, on both sides of the connecting point, have areas about which the shoe halves can spring. The shoe halves may be fitted with reinforcements which ensure that the shoe halves bear against the brake drum in a dimensionally accurate manner. The shoe halves are preloaded with respect to a cam which is directly connected to a brake lever, so that the cam is clamped in between the ends of the shoe halves. Moreover, the ends of the shoe halves are designed in such a manner that the cam is clamped in a contour which provides it with a very specific position in the load-free state. As indicated above, the cam is directly connected to the brake lever and is not mounted in the brake carrier. When the brake lever is actuated, the cam is rotated and the shoe halves are pressed outward against the brake drum, the pressure for the respective shoe, due to the self-centering action of the cam, remaining constant both when the linings are new and after they have been used for a period, involving wear to the linings.
It is also possible to divide the surrounding lining into two lining halves, so that there is a slight saving on material, although this may be of no consequence when fitting the brake with centering of the shoe element. When the shoe element is being fitted on the brake carrier, it is necessary to fit the shoe element in combination with the brake lever, since the brake carrier has an extension which fixes the brake lever in its installed position so that it cannot fall out during use. The extension may be designed in such a way that there is no possibility of removing the brake lever. If the holder is screwed to the brake lever, the shoe element can be removed from the brake carrier with the brake lever and disassembled into its individual parts.
The brake device is designed for inexpensive production. Accordingly, the shoe element may be produced from a deep-drawn piece of sheet metal, the holder being an integral component of this deep-drawn part. The bottom of a deep-drawn cup is stamped out in such a manner that the reinforcements of the shoe halves and the holder with its centering and attachment options are maintained, and both the connecting point and the areas for spring preloading of the shoe halves can be formed. The contact points between the shoe halves and the cam, which are situated approximately opposite the connecting point, are likewise formed by the stamping operation, during which it may be necessary to part the edge at the outer periphery separately, the width of the gap provided for the parting being dependent on the preloading required for the shoe halves.
As an alternative to the above-mentioned brake device made from a deep-drawn piece of sheet metal, the brake device can be made from lightweight metal and is produced as a solid part in which the reinforcements on the shoe halves may be designed with a moment of resistance which satisfies the particular requirements imposed on the braking operation executed by the individual shoe halves. In this way, the trailing shoe half can act with a higher pressure and the leading shoe half with a lower pressure during the braking operation. Since under certain environmental conditions, particularly when wet, drum brakes react more sharply than when it is dry, the moment of resistance can be designed in such a way that a self-energizing effect all the way through to self-locking cannot occur even under adverse environmental conditions.
Since it is necessary for the shoe element to be accurately centered with the brake drum, the holder may have a centering hole which is centered on an axle of the hub of the wheel. A second possibility is for the centering means with respect to the hub axle to be contained in the brake carrier, in which case it is merely necessary to fix the shoe element in an accurate position on the brake carrier. Such fixing may be effected via the holes for attaching the holder to the brake carrier.
Therefore, it is an object of the invention to provide a brake element which can be produced at low cost while dispensing in particular with pivotable bearings for the shoe element and the brake lever.
The various features of novelty which characterize the invention are pointed out with particularity in the claims appended to and forming a part of this specification. For a better understanding of the invention, its operating advantages and specific objects obtained by its use, reference should be had to the accompanying drawings and descriptive matter in which there is illustrated and described a preferred embodiment of the invention.